The following Note outlines some guidelines to the mechanisms available in upgrading the Oracle E-Business Suite and the Oracle Database while considering platform migration.
R11i / R12: Oracle E-Business Suite Upgrades and Platform Migration (Doc ID 1377213.1)
Ideally you can consider the platform migration first then database upgrade
Interoperability Notes EBS 12.0 or 12.1 with RDBMS 12cR1 (Doc ID 1524398.1)
Hope this helps.